artik053: modify ram size

artik053: modify ram size

The SRAM size of TizenRT was incorrectly indicated. Change OS size
information to 946K. (R4 model => OS + Shared Mem + CM0)

 Vector Table : 0x02020000--0x02020FFF (4K)
 Reserved     : 0x02021000--0x020217FF (2K)
 BL1          : 0x02021800--0x020237FF (8K)
 OS           : 0x02023800--0x020E7FFF (786K)
 Shared Mem   : 0x020E8000--0x020E9FFF (8K)
 CM0          : 0x020EA000--0x0210FFFF (152K)
 Wifi         : 0x02110000--0x0215FFFF (320K)
(referenced to samsungartik/tizenrt : commit e7ccbb3beb06730f1623b162c19741fcc63343b7)